High-pressure studies on fused salt systems. Activation volumes for electrical conductance of fused alkali-metal nitrates

Abstract

The isothermal pressure dependence of the specific electrical conductance of fused alkali-metal nitrates has been measured to over 1000 atm and 450°C. Externally heated pressure vessels were used and the system was pressurized with argon. The precision with which the pressure and temperature could be controlled and measured was considerably greater than in any previously reported work. Particular care was taken to prevent the solution of argon in the melts. The values of –RT(∂ ln x/∂P)T obtained for LiNo3, NaNO3, KNO3, RbNO3 and CsNO3 were respectively –0.8, 2.6, 5.7, 6.5 ml mole–1(all at 400°C) and 6.9 ml mole–1(at 450°C). In all cases a slight temperature dependence of about –0.005 ml mole–1°C–1 was observed. Approximate values of the isochoric activation energy are derived. This allows the isobaric activation enthalpy to be resolved into two terms, whose relative importance varies systematically as the cation radius is increased.